Hip joint prosthesis

ABSTRACT

A ball-shaped portion is to form part of the hip joint and a second portion extends from this ball-shaped portion and is to be inserted into an opening in an human femur. The second portion is provided with a passage through which an elongated expander rod is extended which is also to be inserted into the opening of the femur, and on the expander rod is arranged a series of expansion elements in form of a row which, as the expander rod is moved longitudinally of the row, are all expanded to anchor the prosthesis in the femur.

[111 3,846,846 [451 Nov. 12,1974

United States` Patent [1914 Fischer 12S/92 BCBenjamin.,.,...,.............. Hermg 2 714 749 2/1956 2,998,007 8/ l 9613.283.640 ll/l966 9, 2 .m s rl e .m e h n s A, a E h mm w mm A T .Nl OmJm wv Hm MM 5..7L

D-724l Tumlngen, Germany sept.26, 1973 Primary Examiner-Richard A.Gaudet Assistant Examiner-J. Yusko [22] Filed:

Appl NO': 401103 Attorney, Agent, or Firm-Michael S. Strikcr HIP JOINTPitosTHEsls` Background rof the Invention The present invention relatesgenerally to a surgical prosthesis, and more particularly to a hip jointprosthesis.

There are instances where a hip joint prosthesis is required, forinstance in the event of destruction of the ball ofthe hip joint whichmay be the result of arthrosis. Hip joints for this purpose are alreadyknown. The problem with the prior-art constructions is primarily e themanner in which they must be anchored in the femur. Most commonly usedheretofore has been a method involving the cementing of a portion of theartificial hip joint into the channel of the femur. lt is known to use aspecial cement for, this purpose," namelymethylmentharcrylate.Unfortunately, when this cement hardens afterhaving been applied, it tends to develop a not inconsderable amount ofheat. This, in turn, can be dangerous in the particular area in which ahip joint prosthesis-which is, after all, the articulation betwe1. th9femur and the .iiuwminate bene must be installed and which could lead todamage to the bone substance and to adjacent tissue. For this reason,special complicated measures must be taken by the surgeon to cool andthus protect the bone substance and the adjacent tissue during theliberation of heat resulting from hardening of the aforementionedcement. t

This is evidently highly undesirable, and a further disadvantage isadded to this prior-art approach, namely An additional object of theinvention is to provide such a hip joint prosthesis which affords auniform pressure distribution upon the femur, so as to protect the bonematerial as much as possible against damage and to prevent shifting ofthe prosthesis into the bone under simultaneous destruction of the bonesubstance.

ln keeping with the above objects and with others which will becomeapparent hereafter, one feature of the invention resides in a hip jointprosthesis, which,

brief'ly stated, comprises first means including a ball' shaped portionwhich is to form part of the hip joint, and a second portion which is to`be inserted into the human femur and extends from the first portion.Second means is provided for anchoring the second portion in the femur,and this second means comprises an elongated expander rod insertablethrough the second l portion and into the femur longitudinally thereof,a row the fact that the constant stresses to whichthe artificial hipjoint will be exposed after installation, lead to a loosening of thecemented-in portion of the joint-and v to a constant if slow sliding ofthe joint deeper into the femur. The prior art has attempted to avoidthis, or at least to reduce it, by providing at the junction of theballshaped portion of the prosthesis and of the portion which isinserted into the channel of the femur an abutment surface whichprovides anabutment for the prosthesis against the corticalis of thefemur. However, in the long run this also is not sufficient to preventthe undesired shifting of the prosthesis with reference to the femur, sothat over a period of timek the bone becomes damaged. Of course, whenthis takes place, the prosthesis becomes unuseable. Aside from the factthat this would at the very least involve a further operation to insertanother prosthesis, there exists the danger that the femur may havebecome damaged to such an extent that it is incapable of supportinganother prosthesis.

SUMMARY OF THE INVENTION lt is, accordingly, a general objectof thepresent invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provideanimproved hip joint prosthesis which avoids the aforementioneddisadvantages. 'e

Still more particularly, it is an object of the invention to providesuch an improved hip joint prosthesis which can be readily inserted andanchored in the femur without any difficulties. l

Another object of the invention is to provide such a hip jointprosthesis which can also be readily removed, for instance in the eventof infection.

of tubular expansion elements each surrounding the rod and beingangularly displaceable with reference to the longitudinal-axis of thesame, and actuating means for effecting axial movement of the rod withreference to the row and for thereby causing expansion of the expansionelements into anchoring contact with the. fe-

mur.

The axially successive expansion elements of the row of such elementscooperate with one another, so that each of them expands on axiallyadjacent one, with the leading element of the row becoming expanded byan expander portion which is provided at the leading end of the expanderrod and which is drawn into the leading element. The number of elementsin the row can of V.course be selected at will, for instance independence upon the size and/or weight of the patient on whom theoperation is to be performed, or upon other factors such as theactivities to be performed by the patient. lt might be conceivable touse a single expansion element instead of 'a row of them. However, insuch case, the entire outwardly directed force resulting from expansionof the expansion elements and which acts upon the surrounding bonematerial, would all be concentrated upon a very small area of the boneand would very likely crack the bone. With the arrangement according tothe present invention, however, the pressures resulting from expansionare distributed over several areas of the bone which ar-e spaced fromone another, so that no particular area is subjected to unduly highpressure and cracking of the bone need not be feared. Moreover, thetubular expansion elements can be permitted to become angularlydisplaced with reference to the longitudinal axis of the expander rod,so that they can more readily adapt themselves to the contour of thebone channel, that is the channel in the femurwhich, as is well known,is av hollow bone. The channel is usually somewhat curved, and this alsomilitates against the use of a single and rather long expansion element,so that the insertion of a row of shorter expansion elements is muchsimpler and in many instances is the only manner in which such elementscan be inserted at all. The outer diameter of the expansion elements inthe unexpanded condition thereof, may` but need not-be so selected as tocorrespond to the inner diameter of the channel in the bone. Even ifthis is not the case and the channel is rather large in its diameter ascompared to the tubular expansion elements, a reliable anchoring isstill obtainable because the indi- 3 vidual elements can thenengage theinner wall bounding the channel, in zig-zag fashion.

When the individual expansion elements are expanded, they each form withrespect to the axially pre-` ceding element a step at which they diginto the wall of the bone. These various steps in conjunction with thefrictional engagement of the elements against the bone wall, prevent theundesired lowering of the prosthesis into the bone that is the gradualsliding of the prosthesis axially of thefbone with the resultantdestruction of the material of the bone. This means that the position ofthe prosthesis with reference to the femur remains the same, even over aprolonged periodof time and under constant stress. lf the individualexpansion elements are so turned with reference to one another, that isangularly offset relative to one another, that their axially extendingslots which are provided to facilitate expansion are offset through90from element to element, the formation of the steps and the distributionof the pressure can be further improved.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims.

The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is an axial section through theupper portion of a human femur, showing a hip joint prosthesis ac.

cording to the present invention anchored in the bone; and

FIG` 2 is a fragmentary axial sectional detail view, showing the leadingone of the expansion elements of FIG. 1 in expanded condition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now tothe specificembodiment illustrated in FIGS. l and 2, it will be seen that referencecharacter F designates the femur, that is the tubular bone in which thenovel prosthesis is to be anchored. The prosthesis is designated in totowith reference numeral l The trailing end of the element 9b is in turndrawn into the leading end of the next adjacent element 9 which isexpanded as a result of this, and this continues from element to elementuntil finally the trailing element 9a is also expanded. j

Each of the elements 9, 9a and 9b is provided with at least one axiallyextending slot l0 extending from its respective leading towards itstrailing end to facilitate the desired expansion. The number and axiallength of these slots l0 depend upon the hardness and resistance of thematerial to spreading of the elements 9, 9a and 9b. If, for instance,titanium is used, which is a material that is widely favored for suchsurgical insertions but is difficult to work, the simplicity ofconfiguration of the expansion elements and consequently, the simplicityof the manufacture of them, is advantageous. The extent to which theelements 9, 9a and 9b can be angularly displaced with reference to thelongitudinal axis of the rod 7 depends upon the difference of thediameter of their central passage ll on the one hand, and the outerdiameter of the rod7 on the other hand. Alarge difference provides for asignificant angular displaceability and a small difference for a lesserdisplaceability. The

and has a ball-shaped portion which is to form part of the hip-joint,and a second portion which is to be inserted into the femur F as shown,and which extends from the firstl portion at an angle thereto. Theportion 4 is provided with a bore as illustrated, and it has an end facewhich faces outwardly away from the femur F, and against which the headof a hollow cap nut 6 abuts, the cap nut 6 constituting the actuatingmeans which meshes with external screw'threads on the trailing end of anexpander rod 7 to thereby draw the rod outwardly, that is upwardly inFIG. l, to effect expansion of the expansion elements. The leading endof the rod is provided with an expander portion 8 of the illustratedconfiguration (compare FIGS. 1 and 2).

The rod is surrounded by a row of tubular expansion elements, includinga trailing expansion element 9a, a leading expansion element 9a which islocated adjacent the expander portion 8, and intermediate expansionelements 9. When the rod 7 is drawn upwardly in FIG. l by requisiteturning of the nut 6, the'expander portion 8 is drawn into the element9b, expanding the same.

particular relationship will be selected by the surgeon in dependenceupon the diameter and the curvature of the channel in the femur.

The passages l1 through which the rod 7 extends conically diverge in thedirection towards the respective leading end, thatis downwardly in FIG.1 and in FIG. 2, so that the trailing end of each axially followingexpansion element can enter into the passage of each preceding element.The trailing ends, incidentally, are part-spherical `in'configuration asindicated by reference numeral 12, to facilitate their introduction intothe passages 11, and to reduce the force which is applied to be exertedfor spreading'purposes by the rod 7. Furthermore, this also facilitatesthe angular displacement ofthe expansion elements with reference to thelongitudinal axis of the rod 7.

When the rod 7 is drawn upwardly in FIG. 1 by turning of the `nut 6, theelements 9 can accommodate themselves to the curvature of the passage inthe femur F by angularly shifting about the longitudinal axis of the rod7. This means that if the width of the bone passage is greater than theexpansion capability of the elements 9, the latter can assume a zig-zagshaped configuration' in that alternated ones of them become inclined toopposite sides of the rod 7. In this manner, the arrangement can stillbe reliably anchored due to the wedging action resulting from suchinclination, in which the opposite axial ends of the respective elements9 become wedged against the bone at opposite sides of the passage.

lf the channel 14 in the femur F is curved to a substantial extent, afurther improvement in the accommodation of the elements 9, 9a and 9b tothis curvature can be achieved by making the rod 7 itself curved, inaccommodation vto the curvature of the channel 14. As a general rule,all channels in the various femurs are curved lto a greater or lesserextent; it is very rare that a completely straight channel isencountered. Curving the rod 7 has the advantage not only offacilitating the introduction of the rod and of the elements 9, 9a, 9binto the channel 14, but also if the latter is curved signifcantly, theangular displaceability of the expansion elements about the longitudinalaxis of the rod 7 is in some circumstances no longer sufficient tocompensate for this curvature.

If the rod 7 is itself curved, then the nut 5 is used so that therod 7need not be turned. It will be appreciated that if the rod 7 is straightor curved only to a very slight extent, it will be possible to eliminatethe nut 6 and instead to merely provide the outer end portion of the rod7 itself with a head having a slot or the like, by means of which therod could be turned due to engagement with an appropriate tool. It wouldthen be this head that would bear against the outer surface of theportion 4. In that case, it will be appreciated that the portion 8 wouldnot be of one piece with the rod 7, but instead the rod 7 would have tobe threaded into the portion 8 and, as the rod 7 would be turned, theportion 8 would be drawn into the leading expansion element 9b, in themanner described earlier.

If, however, the nut 6 is used, then the portion 8 can be of one piecewith the rod 7. In such an instance, which is illustrated in FIGS. 1 and2, the axial length of the nut 6 is somewhat greater than the distancethrough which the nut 6 must be drawn outwardly (upwardly in FIG. 1) toeffect complete expansion of all of the expansion elements 9, 9a, and9b. This assures that the outer end of the rod 7, will be located withinthe central passage of the nut 6 at all times, and that the possiblityof a development of a painful pressure point resulting from engagementof an outwardly extending end portion of the rod with the surroundingtissue is avoided.

The cross section of the portion 4 corresponds at least approximately tothe form of the channel 14 at the upper end of the femur F, which crosssectional conguration is usually somewhat elliptical. Also, the trailingexpansion element 9a is configurated to accommodate itself to theconically converging contour of the channel 14. This facilitates thesupport and anchoring of the element 9a in the channel 14. The trailingend of the element 9a is provided with a recess 15 into which theadjacent end portion of the portion 4 extends, to prevent relativeturning of the element 9a with reference to the portion 4.

The portion 4 extends at an angle of approximately 120 with reference tothe axis of the base part on which the ball-shaped portion 2 is providedand this angle corresponds approximately to the natural angle of the hipjoint. A spring washer or the like can be used intermediate theouterwardly directed surface of the portion 4 and ahead of the rod 7,or, as in the illustrated embodiment, the head of the nut 6, to fix themin place against undesired turning. Such spring washers serve,incidentally, also to compensate for the effect of pulling forces actingupon the rod 7 and provide a certain amount of elastic yieldability whena load is placed upon the hip joint prosthesis.

FIG. 2 shows the leading expansion element 9b in axial section. It willbe seen that it has the portion 8 is drawn into the passage 11 of theelement 9b, the latter is spread apart, Le. expanded, which ismadepossible by the provision of the slot 10. At the same time, the trailingend 12 of the element 9b is drawn into the passage ll of the axiallyadjacent element 9, thereby expanding the latter. As 4this takes placefor all of the elements 9, 9a, and 9b, adjacent elements form steps withone another, which steps are identified with reference numeral 16. Atthese steps the elements bite into the bone material surrounding thechannel 14 and this in combination with the frictional engagement of theouter surfaces of the elements 9, 9a and 9b with the surrounding bonematerial provides for a reliable anchoring and prevents the sliding withreference to the femur, which, as outlined earlier can lead to thedestruction of the bone material.

Undesired relative turning between the rod 7 and the element 9 can beprevented by making the crosssection of the rod 7 and of the passages 11non-circular and mating, without, however, thereby interfering with thedesired angular displaceability of the elements 9. ln the illustratedembodiment a spring portion 17 is provided on the rod 7 which engagesthe corresponding groove 18 of the element 9, as shown in FIG. 2.However, a simple use of a non-circular mating crosssection, forinstance quadratic or the like, can suffice also.

Finally, it is also possible to roughen the outer surfaces oftheelements 9, 9a and 9b for instance by knurling them or by providingfluting or the like to increase the friction betweem them and the bonematerial of the femur F and to thereby improve the anchoring effect.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application of other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in ahip joint prosthesis, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fullyv reveal the gistof the present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim: j

1. A hip joint prosthesis, comprisngfirst means, including a ball-shapedportion which is to form part of a hip joint, and a second portion whichis to be inserted into a human femur and extends from said firstportion; and second means for ranchoring said second portion in thefemur, comprising an elongated expander rod inserted through said secondportion and insertable into the femur longitudinally thereof, a row oftubularexpansion elements each surrounding said rod and being angularlydisplaceable with reference to the longitudinal axis of the same, andactuating means on said expander rod for effecting axial movement ofsaid rod with reference to said row and for thereby causing expansion ofsaid expansion elements into anchoring contact with the femur.

2. A prosthesis as defined in claim 1, said rod having a leading endprovided with an expander portion; and said row including a leadingexpansion member into which said expander portion is drawn in responseto said axial movement.

3. A prosthesis as detined'in claim 2, wherein each of said elements hasa leading end and a trailing end, a

center passage through which said rod extends which conically divergestowards said leading end, and a slot in its peripheral wall extendingfrom said leading towards said trailing end.

4. A prosthesis as defined in claim 2, wherein each of said elements hasa leading end and a part-spherical trailing end, and a center passagethrough which said rod extends and which conically diverges towards saidleading end, said trailing end of each of said elements extending intosaid center passage at the leading end of the respective axiallyadjacent element for expanding the latter, in response to said movementof said rod.

5. A prosthesis as defined in claim 4, wherein said elements have anexterior configuration which coaxially converges toward the respectiveleading end.

6. A prosthesis as defined in claim l, wherein said elements have outersurfaces which are roughened.

7. A prosthesis as defined in claim l, wherein said row includes aleading and a trailing element; and wherein at least said trailingelement has an exterior configuration which conically converges indirection towards said leading element.

8. A prosthesis as defined in claim 1, the femur having a curvedinternal channel; and wherein said rod is and wherein said row includesa leading element, and a trailing element which is adjacent said secondportion, said trailing element having an end face provided with a recessinto which said inner end extends.

l0. A prosthesis as defined in claim l, said second portion extending atan angle to said first portion and having a bore for said rod, and asurface which faces outwardly from the femur; and said rod having anouter end adapted to bear against said surface.

l1. A prosthesis as defined in claim l, said second portion extending atan angle to said first portion and having a bore for said rod, and asurface which faces outwardly away from the femur; said rod having atrailing portion provided with screw threads; and further a cap nutthreadedly engageable with the screw threads of said trailing portionand provided with a head which bears against said surface.

12. A prosthesis as defined in claim 11, wherein said cap nut has anaxial length which is at least equal to the distance through which saidrod must be moved with reference to said row in order to cause saidexpansion of said elements.

13. A prosthesis as defined in claim 1, wherein said elements each havea center passage through which said rod extends, said passages and saidrod having respective non-circular mating cross-sections for preventingundesired relative angular displacement.

1. A hip joint prosthesis, comprising first means, including aball-shaped portion which is to form part of a hip joint, and a secondportion which is to be inserted into a human femur and extends from saidfirst portion; and second means for anchoring said second portion in thefemur, comprising an elongated expander rod inserted through said secondportion and insertable into the femur longitudinally thereof, a row oftubular expansion elements each surrounding said rod and being angularlydisplaceable with reference to the longitudinal axis of the same, andactuating means on said expander rod for effecting axial movement ofsaid rod with reference to said row and for thereby causing expansion ofsaid expansion elements into anchoring contact with the femur.
 2. Aprosthesis as defined in claim 1, said rod having a leading end providedwith an expander portion; and said row including a leading expansionmember into which said expander portion is drawn in response to saidaxial movement.
 3. A prosthesis as defined in claim 2, wherein each ofsaid elements has a leading end and a trailing end, a center passagethrough which said rod extends which conically diverges towards saidleading end, and a slot in its peripheral wall extending from saidleading towards said trailing end.
 4. A prosthesis as defined in claim2, wherein each of said elements has a leading end and a part-sphericaltrailing end, and a center passage through which said rod extends andwhich conically diverges towards said leading end, said trailing end ofeach of said elements extending into said center passage at the leadingend of the respective axially adjacent element for expanding the latter,in response to said movement of said rod.
 5. A prosthesis as defined inclaim 4, wherein said elements have an exterior configuration whichcoaxially converges toward the respective leading end.
 6. A prosthesisas defined in claim 1, wherein said elements have outer surfaces whichare roughened.
 7. A prosthesis as defined in claim 1, wherein said rowincludes a leading and a trailing element; and wherein at least saidtrailing element has an exterior configuration which conically convergesin direction towards said leading element.
 8. A prosthesis as defined inclaim 1, the femur having a curved internal channel; and wherein saidrod is curved in longitudinal direction for facilitating itsaccommodation of said channel.
 9. A prosthesis as defined in claim 1,said second portion having an inner end remote from said first portion;and wherein said row includes a leading element, and a trailing elementwhich is adjacent said second portion, said trailing element having anend face provided with a recess into which said inner end extends.
 10. Aprosthesis as defined in claim 1, said second portion extending at anangle to said first portion and having a bore for said rod, and asurface which faces outwardly from the femur; and said rod having anouter end adapted to bear against said surface.
 11. A prosthesis asdefined in claim 1, said second portion extending at an angle to saidfirst portion and having a bore for said rod, and a surface which facesoutwardly away from the femur; said rod having a trailing portionprovided with screw threads; and further a cap nut threadedly engageablewith the screw threads of said trailing portion and provided with a headwhich bears against said surface.
 12. A prosthesis as defined in claim11, wherein said cap nut has an axial length which is at least equal tothE distance through which said rod must be moved with reference to saidrow in order to cause said expansion of said elements.
 13. A prosthesisas defined in claim 1, wherein said elements each have a center passagethrough which said rod extends, said passages and said rod havingrespective non-circular mating cross-sections for preventing undesiredrelative angular displacement.